1. Field of the Invention
The present invention relates generally to the art of snorkels. The invention relates more specifically to a snorkel that allows mostly "clean" air for inhalation.
2. Prior Art
Most snorkels have a single breathing tube for inhalation and exhalation. The problem with this is that at the end of each exhalation, the air that remains in the tube is the air that has been in the user's lungs the longest. This "used" air has less oxygen and more carbon dioxide than fresh air. With each inhalation, the user first inhales this "used" air and then begins to inhale fresh air once the internal volume of the snorkel has been evacuated. This causes an increased breathing rate and increases the chance of fatigue, dizziness and nausea.
The typical adult snorkel tube and elbow has an internal volume of 8 cubic inches. An adult man typically inhales between 60 and 120 cubic inches of air (1 to 2 liters) with each breath depending on their size and level of exertion. Typical women and children inhale a smaller volume. Therefore, the typical adult man inhales between 6.5% and 13% "used" air when using a regular snorkel. Women and children inhale an even larger percentage of "used" air.
The most obvious solution to solve this problem is to design a snorkel with two tubes that have two one-way valves such as the Wagner snorkel (U.S. Pat. No. 5,664,558). One of the problems with this design is that when the snorkel fills with water such as while descending a few feet, it is impossible to blow the water out of the inhalation tube. The next inhalation draws in water instead of air which can cause choking. Another problem with this design is that the breathing resistance for both inhalation and exhalation is high in a version of marketable size because typical one-way valves substantially reduce the flow area and require a high level of breathing exertion to fully open.
As mentioned in the Wagner patent, a clean air design in the prior art that is coaxial must have a larger outside volume compared to two tubes side by side for equivalent internal volumes for inhalation and exhalation. The Lin co-axial snorkel (U.S. Pat. No. 5,117,817) is both clean air and dry, but is also complex to make and cannot be made small enough to be marketable and have acceptable breathing resistance. As evidence, the Lin snorkel has been on the market for about 6 years, but without the center tube (has a single large tube) so that it does not have the clean air feature. It is only a dry snorkel.
It would be desirable to have a snorkel that reduces the amount of "used" air inhaled, but still has low breathing resistance, a relatively compact size, allows water to be purged out, and has relatively simple construction.